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Old 06-22-2013, 02:17 PM
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No vacuum signal from carb

The engine is a freshly built and broken in olds 403. the carb is the original 800 CFM Quadrajet, rebuilt by everday performance.

My problem is that i'm hooking my vac gauge to ports on the front of the carb but i'm not getting any signal at idle, it sits at 0 on the gauge. when i rev it up the signal bounces up to around 15. I've tried a few different ports with the same results, they can't all be ported/switched sources of vacuum are they?

I have my vacuum advance hooked to a manifold source of vacc, when i head back to the garage i'm going to try taking a reading directly from the manifold.


I just re-lashed the valves again, i thought i might have had them set wrong but it didn't seem like it. I use the preload method that comp cams recommended i do. tighten to 0 lash, then + 1/2 turn. One of the notes with my cam was tighter lash.

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Old 06-22-2013, 05:05 PM
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Ok the ports i was trying to pull a reading from are ported, problem solved.
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Old 06-22-2013, 10:08 PM
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Depending on the year, one of the vacuum ports could have been for the EGR. Similar in some ways to a ported source, but not quite. These cause trouble when used for the vacuum advance.
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Old 07-10-2013, 01:00 AM
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this helps explain the ports a little better

http://home.comcast.net/~kc8oye/Engine/ported_vac.jpg
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